A variable-speed pumped storage power generation apparatus in a power generation mode adopts a method in which a pump turbine is in charge of controlling rotational speed in accordance with the power and the head and a generator motor is in charge of power control that causes the power to directly follow a power output command from the outside. Such a method can obtain a quick power response close to the power output command, but the speed control depends on the flow control on the side of the pump turbine with a slow response; therefore, speed fluctuations and overshoot are inevitable. Accordingly, a conventional variable-speed pumped storage power generation apparatus adopts protection control such as a method of preventing the slip frequency from exceeding the limit of the variable speed range by adding a power output correction command, which is defined in accordance with the rotational speed or slip frequency, to the power output command when the slip frequency approaches the limit of the variable speed range.
Patent Literature 1 below describes the method of preventing the slip frequency from exceeding the limit of the variable speed range by adding the power output correction command.
FIG. 3 is a diagram illustrating a configuration of a variable-speed pumped storage power generation apparatus described in Patent Literature 1. FIG. 3 illustrates a generator motor 1. The generator motor 1 is rotationally driven by a pump turbine 2 directly connected to a rotor and at the same time performs a variable speed operation such that a secondary winding 1b of the generator motor 1 is supplied with an AC excitation current adjusted to a predetermined frequency in accordance with rotational speed N of the generator motor 1 from a secondary excitation controller 3 equipped with a frequency converter and AC power at the same frequency as the frequency of an AC system 4 is output from a primary winding 1a of the generator motor 1.
FIG. 3 further illustrates a turbine characteristic function generator 5. The turbine characteristic function generator 5 receives a power output command Po and a water level detection signal H from the outside, and generates an optimum rotational speed command Na and an optimum guide vane opening Ya to perform operation with the maximum efficiency. FIG. 3 further illustrates a rotational speed controller 16. The rotational speed controller 16 compares the optimum rotational speed command Na with the actual rotational speed N detected by a rotational speed detector 6 and outputs a guide vane opening correction signal ΔY. The optimum guide vane opening Ya from the turbine characteristic function generator 5 is input to an adder 21 together with the guide vane opening correction signal ΔY to be input to a guide vane driving unit 10, whereby the guide vane driving unit 10 controls a guide vane 11.
FIG. 3 further illustrates a slip phase detector 7. The slip phase detector 7 detects a slip phase Sp that is equal to the difference between the potential phase of the AC system 4 and the secondary rotational phase of the generator motor 1 expressed in electrical degrees. The slip phase Sp is input to the secondary excitation controller 3. In addition, the rotational speed N detected by the rotational speed detector 6 is input to a power output command correction unit 25A.
The power output command correction unit 25A maintains an output signal thereof at zero when the rotational speed N is between set values Nklg and Nkug, reduces the output signal in proportion to the decrease in the rotational speed N when the rotational speed N falls below the set value Nklg, and increases the output signal in proportion to the increase in the rotational speed N when the rotational speed N exceeds the set value Nkug. This operation is referred to as speed protection control. The output signal of the power output command correction unit 25A is input to a transient characteristic adjuster 25B, which adjusts responsiveness and stability of the speed protection control system performed via the secondary excitation controller 3. FIG. 3 illustrates a first order lag element as an example of the transient characteristic adjuster 25B. Note that a reference character S denotes a Laplace operator. FIG. 3 further illustrates an adder 26 that adds an output ΔP1 of the transient characteristic adjuster 25B and the power output command Po provided from the outside together to produce a generator motor output command Pg.
The generator motor output command Pg and the slip phase Sp of the slip phase detector 7 are input to the secondary excitation controller 3. The secondary excitation controller 3 controls an AC excitation current supplied to the secondary winding 1b of the generator motor 1 such that a detected output signal P of the generator motor 1 detected by an active power detector 9 is equal to the generator motor output command Pg.
The variable-speed pumped storage power generation apparatus described in Patent Literature 1 with such a configuration can greatly reduce a transient overshoot of the rotational speed in an opposite direction with respect to a sudden increase or decrease in the power output command Po.